Unless one wants a yard of sand, rock, and scattered creosote bushes, it takes water and some sort of irrigation system. My mother loved to go out early in the morning, turn on a faucet and greet the sun, hose in hand, as she watered plants. I have a much larger yard than she did, and prefer to sleep late. So I let my automated system do the watering.
The first few years, I asked nursery men and landscapers, lawn maintenance crews and horticulture experts -- How long do I run my lawn sprinklers and how often? How long do I run the bubblers in my orchard and how often. Their answer was always, "That depends." They said that I should observe the plants and I would know when they weren't getting enough water. So 10 years and many dead plants later, I am just beginning to get the information to figure it out. And by the way, most of my plants died from underwatering, not overwatering as the experts predict. After all, I moved here from a very wet and humid Arkansas, so my tendency was to underestimate supplemental water needs in this windy arid climate. very time it rains in Barstow, it is amazing how my plants perk up. And every tine it rains in Barstow, I think that I can turn off my watering system, but that is only true for the lawn and low water plants. It doesn't rain very often, and when it rains, it doesn't rain very much. At least not where I live.
What I already knew:
1 cu. ft. water = 7.4 gal.
1 gal. water = 0.135 cu. ft.
1 sq. ft. water 1 inch deep = .62 gal.
1 gal. water = 1.62 sq. ft.-in.
What I have learned recently thanks to Dave Palumbo of Rainbird and Victor Valley College:
sprinklers spread 1.58" water per sq. ft. per hr. which is 0.98 gph
1 bubbler emits 1-2 gpm (gallons of water per minute)
1/2" polyethylene irrigation tubing should be limited to 4 gpm,
also 1//2" PVC pipe
How much it delivers depends on what is connected to it.
e.g. 4 bubblers max
1/2" soaker hose delivers 1 gph of water per foot
i.e. A 60' foot soaker hose = 1 bubbler,
but delivers the water over a greater area
1/2" dripline delivers 0.6 gph or 0.9 gph per inline emitter,
The emitters are spaced every 12", 18" or 24"
i.e. A 100' dripline with 0.6 gph emitters every 12" = 1 bubbler,
but again over a greater area
1/4" irrigation tubing should be limited to 17 gph
1/4" soaker tubing delivers 0.33 gph per foot
1/4" dripline delivers 0.5 - 0.8 gph from each inline emitter,
The emitters are spaced every 6" or 12"
At most 35 emitters can be used
The problem of course is that knowing how much water the irrigation system delivers, still does not tell us how long it should run and how often. For example, if Barstow averages 4" rain per year, then that is all the water native plants should need, or maybe a little more to perform well if they are close together. But obviously dumping 4" of water on them on August 12 isn't going to do it. Nor will giving them 1/3" of water on the first of each month.
It helps to know that trees need the water to reach roots at a 3' depth
shrubs at a 2' depth
annual & perennials at a 1' depth
lawn at a 0.5' depth
And we need to know whether the soil is sand, loam, or clay. My soil is sand, but some parts of Barstow have clay. Water penetrates the different kinds of soil differently.
sand 1" water penetrates 12"
loam 1" 8"
clay 1" 4"
So more water must be applied to clay soil to reach a certain depth, than to sandy soil. But clay soil holds the water longer, so it does not to be applied as frequently. Also, in clay soil the water spreads almost as far as it penetrates. In sandy soil it penetrates twice as far as it spreads. Therefore bubblers or whatever can be farther apart if the soil is clay than if it is sand. The ideal of course is to build up the soil to where it is all loam.
The factors that influence irrigation runtime and frequency are: plant type, planting density, climate, microclimate, soil type, time of year, weather, and type of irrigation delivery system. Rather than go through all of the calclations here, I'm going to give some formulas and tables for watering that I have worked out. Take them with a grain of salt and if they work, let me know. Most of the factors have values that are guesstimates at best, although gesstimates of the experts, not me.
select a value from each category:
plant water needs plant form
p = 0.2 drought tolerant f = 0.3 grass
0.5 moderate water 0.6 annual or perennial
0.8 regular water 1.2 shrub
1.9 tree
type of irrigation
i = 2.55 gph sprinkler
60.0 gph bubbler at 1 gpm
1.0 gph soaker hose
0.6 gph inline emitter 1/2" dripline
0.5 gph inline emitter 1/4" dripline
Assuming each type of irrigation is on a separate valve, then with sandy soil, the runtime for the valve should be
T = 60 x f / i minutes
This is true year around as the water always needs to penetrate to the root zone of the plant. Obviously when it is windy, more water is needed and when it is raining, less water is needed.
T(minutes) grass annual shrub tree in sandy soil
sprinkler 7 14 20 45
bubbler 0.3 0.6 1.2 1.9
soaker hose 18 36 72 114
1/2" dripline 30 60 120 190
1/4" dripline 36 72 144 228
This table assumes there are enough sprinklers, bubblers, emitters, etc. to cover the area under the plants.
The amount of water a plant needs each month depends on the evapotranspiration rate. I am using the seasonal rates for Barstow.
evapotranspiration
e = 1.67 gal.. per month cold weather
4.09 gal. per month mild weather
5.58 gal. per month hot weather
Then the frequency of watering is
F = e x p / f times per month
or
every 30 / F days
For clay soil the runtime should more or less be doubled and the frequency halved.
F (regular water) cold mild hot
(times per month)
grass 5 11 15
annual/perennial 3 6 8
shrub 2 3 4
tree 1 2 3
New plants should be watered more frequently: new trees or shrubs with the frequence of annuals, and new annuals with the frequency of grass, because the roots have not yet reached the standard depth for the form of plant.
Note - I got my basic information from a course in irrigation at Victor Valley College this Fall. The formulas and tables are my own. I have not yet gone through a year using these figures although I am going to do so. Next year I will let everyone know how they work.
Evapotranspiration rates for Barstow
month inches per month gallons per month per square foot
Jan. 2.2 1.36
Feb. 3.09 1.92
Mar. 5.13 3.18
Apr. 6.6 4.09
May 8.81 5.46
June 9.21 5.71
July 9.4 5.83
Aug. 8.18 5.07
Sept. 6.38 3.96
Oct. 4.76 2.95
Nov. 2.83 1.75
Dec. 2.07 1.28
cold 2.7 1.67
mild 6.6 4.89
hot 9 5.58
.
No comments:
Post a Comment